Calculating Dynamic Disturbance Rejection Measures

A number of indicators for the determination of the disturbance rejection capability of a system have been proposed in the literature in the last two decades. These tools are useful for evaluating early stage process designs and screening regulatory control structures, since they are based on minimal modelling requirements. In previous publications (Hovd and Braatz, 2000; Hovd et al., 2003; Kookos and Perkins, 2003), it has been shown how to evaluate at steady state the disturbance rejection measures proposed by Skogestad and Wolff (1992). If acceptable values for these disturbance rejection measures are not achieved, no controller can achieve satisfactory control. In this paper, it is shown how to obtain upper and lower bounds for these disturbance rejection measures also as a function of frequency. The upper and lower bounds can be made arbitrarily accurate at the expense of increasing the size of the optimization problems involved. Copyright c 2005 IFAC